Certain atmospheric conditions can lead to ice formation on aircraft surfaces. Ice formation on aircraft surfaces can increase the weight of the aircraft and can increase the drag of the aircraft. Increasing either the weight or the drag of an aircraft can result in a stall speed that is higher than it would otherwise be in an ice-free condition. Ice formation on lifting surfaces can result in a decrease in a wing's lift and/or a decrease in a propeller's thrust. Ice formation can also affect the controllability of an aircraft by affecting the airflow over control surfaces, such as ailerons.
Various atmospheric conditions can cause more or less ice formation on an aircraft. For example, water droplet density, total moisture content, air temperature, water droplet temperature, droplet size distribution, etc. all factor into risk of ice formation. Some atmospheric conditions can present little or no risk of ice formation on an aircraft.
Various aircraft flying conditions can affect locations and/or amounts of ice formation on aircraft surfaces. For example, airspeed, angle of attack, angle of side-slip, and presence of de-icing equipment all factor into location and/or risk of ice formation.
Some aircraft have been equipped with equipment intended to obtain various metrics of the atmosphere so as to predict whether the atmosphere presents a risk of ice-formation on exterior surfaces. Ice formation on aircraft surfaces can be visually perceived by the pilot, should the ice form on a surface within view of the cockpit window.